In order to monitor the screwing torque applied to screw caps on bottles, known devices exist with friction clutch means under elastic loading, which act basically as torque limiters. When the tightening torque varies the said elastic means must be adjusted. These known devices are not capable of producing operating conditions that are constant over time because of the variable reaction of the friction clutches in response to temperature, wear and other factors. Other known devices use dog clutches instead of friction clutches, loading them by pneumatic pressure which is variable in accordance with tightness requirements: when the desired screwing torque is reached one of the their components makes an axial movement which is detected by sensors so that the degree of tightness of the cap can be checked. The operation of these devices is however once again unreliable and inconstant over time as it again depends entirely on a clutch of the friction type.